The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Sydney murder accused 'acted on orders'

A man accused of a double murder inside a meth lab in suburban Sydney was acting on the orders of the woman at the top of a drug syndicate, police will allege.

Kevin Ly stepped into the dock at Fairfield Local Court on Tuesday morning and smiled at friends in the public gallery.

He made no application for bail and it was formally refused by Magistrate Vivian Swain.

The unemployed 25-year-old looked towards his supporters and raised his handcuffed arms in a parting gesture as he was led back to the cells.

Ly is charged with murdering Son Thanh Nguyen, 39, and his girlfriend Thi Kim Lien Do, 35, in 2013, before wrapping their bodies in bedsheets and dumping them in separate locations.

Investigators believe Mr Nguyen was a methamphetamine "cook", and that he and Ms Do were murdered inside a Canley Vale rental home that doubled as a clandestine laboratory.

"She (Ms Do) may well may have been in the wrong place at the wrong time, but certainly our information is that Mr Nguyen was involved in a dispute with a group which has led to his death over drugs," Detective Superintendent Mick Willing told reporters earlier in the day.

Police say Mr Nguyen and Ms Do were last seen alive on April 10, 2013.

It is alleged that Mr Nguyen had stolen a quantity of methamphetamine from his female boss, and that Ly - the woman's "henchman" - had lured him back to the Canley Vale house that day on her instructions.

It will be alleged that after the pair arrived at the property Ly emerged from a bedroom with a shotgun, flanked by two others armed with a samurai sword and a revolver.

Investigators believe both deceased were bound and that Ms Do was heard pleading: "Please forgive me. I didn't do anything. I know nothing. Please don't kill me."

In another room, Mr Nguyen's boss is said to have warned him: "Return it. If you return it, Lien will stay alive. If you did it, you have to bear the consequences."

Moments later, it is alleged, she turned to Ly and said: "Just do it."

Police will allege she then handed one of Ly's associates a case of $50 notes as payment for the murders.

It will be alleged Ly then ordered one of his male associates to help dispose of the bodies, saying: "You have to do it for me to trust you."

Police documents viewed by AAP reveal that a key piece of evidence - a photograph showing the suspected syndicate boss's car parked outside the Canley Vale house on the day of the murders - was unearthed because a Google Street View camera happened to pass through on that day.

Late on April 10, an off-duty ambulance officer was driving through Bankstown when she spotted a pair of legs poking out of a pile of sheets on the side of the street.

The grim bundle hid Mr Nguyen's body; his wrists were tied behind his back with cable ties and blood-soaked tissues were stuffed in his mouth.

The day after Mr Nguyen's body was discovered, his girlfriend was reported missing.

But her fate was not known until early 2014, when a home owner repairing a fence near West Hoxton came upon what he thought was a dead animal. What he found instead was a human skull, wrapped in bedding.